1. Field of the Invention
The present invention relates generally to a forging die, and more specifically to a structure of the forging die to manufacture a part having a plurality of internally-tapered grooves, for instance, such as a socket with a plurality of inner races used for a constant velocity joint or a universal joint.
2. Description of the Prior Art
There are some mechanical parts which are difficult to manufacture by using a simple forging die because of their complex structure.
The typical example among these parts is a socket used for a constant-velocity joint or a universal joint.
The socket is usually provided with a plurality of inner races along which ball bearings are rolled. Since it is necessary to form a plurality of inner races on the inner spherical surface thereof, the inner races inevitably take the form of roughly-semicylindrical grooves tapered internally with respect to the axis of the part, that is, in the stamping direction when manufactured by forging.
In order to manufacture such a mechanical part as described above in the prior-art method, the blank is first preliminarily formed into a predetermined shape such that the lower portions of the semicylindrical grooves are straight, and next the lower portions thereof are stamped from the outside or bent inwards by applying a force thereto.
In this prior-art manufacturing method, however, since the width of the groove is susceptible to change due to the stamping force, an additional cutting step or grinding step is required to obtain the preferred accuracy for the part, thus resulting in the need for a great number of manufacturing steps with their resulting high cost.
To partially overcome these problems, it is known to use a special forging die, provided with a plurality of liner-grooving dies arranged in the lower die so as to pivot in the radially inward direction thereof, as described in Japan Patent Publication No. S52-24978. In this prior-art forging die, a mechanical part with internally tapered grooves can be forged in a simple process; however, a relatively great forging stroke length is required due to the structure thereof.
A more detailed description of this prior-art forging die will be made hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.